Recently David Vizard sent a note asking on behalf himself and Mike Jones if I would act as referee for the BBC cam shootout for Davids book. To David and Mike thank you regarding my integrity. Now here are the Specs as they mailed them to me.Stuart Smith

David Vizard Specs

Stuart,

Cam shootout specs - here they are -

These are from a list of profiles from Mikes library or lobes based on such.Mike did say he would design additional profiles as required here.Here is what my Cam Master program calls for with the spec of engine being built.

dbusch wrote:i just wonder how the piston to valve clearance and the base circle will turn out. my calcs show a .890 base circle.

These would be my concerns also. With a .480 lobe on a std bbc core it is getting way too small. There is going to be a lot of deflection with the core.

What are the valve spring specs that will be used? What is be the pushrod diameter and thickness?

Its hard to tell without working it out on the dyno but with 15:1 compression I would think that the intake cam centerline will be no more than 109, maybe straight up. The tappet lift at TDC should be close to .165 for the 282 and .170 for the 284 installed on 110 intake centerline. That's not terrible for p/v clearance.

Some very good cam pickers. Going to be interesting. The two cams are so similar the performance should likewise be similar. Odds are the engine will make nearly identical power/torque all the way through the range.

dbusch wrote:i just wonder how the piston to valve clearance and the base circle will turn out. my calcs show a .890 base circle.

These would be my concerns also. With a .480 lobe on a std bbc core it is getting way too small. There is going to be a lot of deflection with the core.

What are the valve spring specs that will be used? What is be the pushrod diameter and thickness?

Its hard to tell without working it out on the dyno but with 15:1 compression I would think that the intake cam centerline will be no more than 109, maybe straight up. The tappet lift at TDC should be close to .165 for the 282 and .170 for the 284 installed on 110 intake centerline. That's not terrible for p/v clearance.

Some very good cam pickers. Going to be interesting. The two cams are so similar the performance should likewise be similar. Odds are the engine will make nearly identical power/torque all the way through the range.

i wonder if it will be A, B, A, B, test method and if the engine be run in first with a milder cam to seat everything?

dbusch wrote:yup, the core will be very flimsy lol. A SBF std core is about the same as a BBC, and i wont go over .490 lobe lift on those.

the cam is not a bad choice since the heads are a limitation for a 565 trying to make peak power past 7K. but, i would have gone with at least 112 or 113 lobe sep with intake at 110.

the two cams are too close together to bother with. they should grind one on 113 to make it a more meaningful test.

I don't think they are testing camshafts. I think they both want to make more power than the other one, and neither wants to lose. Vizard's program came up with one cam, Mike's program came up with another. Yes, they are very similar but neither one knew what the other was doing and that's how it worked out.

dbusch wrote:i just wonder how the piston to valve clearance and the base circle will turn out. my calcs show a .890 base circle.

The Base Circle will be .900" +.000"/-.001".900" is the barrel diameter on the cores we use for cams with more then .480" lobe lift, so the cam won't flex any more then it would with a .480" lobe.

so you are comfortable with .525" lobe lift on that core? maybe the cam wont flex any more, but the pressure angle is going to be severe. I think you guys should stop at .495 lobe lift with the std core, and go .525 when you go with the 55mm core. that makes more sense to me, and people reading the magazine wont be shaking their head in disbelief.

Using the DV LCA chart from his book, he should have picked a LCA at 104-105º for this engine. The 565ci engine with only a 2.35" intake valve puts the CID/ValveDiam (30.05) off the chart on the left at 98-99ºLCA with an adjustment of +2º for the valve arrangement and +3.5º for the 15:1 compression ratio.

Hmmm .... wonder why he didn't spec the cam the way his book proclaims is the way to do it based on the results of thousands of dyno tests?

I can't imagine an engine like that wanting a 104-105LCA, but that's what his book would lead you to believe.

you also need to add for the 1.8 rocker ratio (vs. 1.5 the chart was written around) not to mention the high compression allows for much longer exhaust duration and earlier exhuast valve opening which is also explained in the book. Earlier exhaust valve opening = wider LSA. As David explained it to me, once the compression crosses the 14.5-15:1 range, they become much more sensitive to having too narrow of an LSA (which is the inverse of a 10.5:1 motor). Also with this engine being under-valved and under-flowed in every aspect they need the exhaust duration to get it to "hang on" at upper rpm as well as possible. I believe that is why the compression ratio is so important to the overall combination.